This invention relates generally to waste treatment apparatus, and more particularly to thermo-oxidizer evaporators.
Waste water streams pose particular challenges for efficient and effective disposal. Environmental concerns prevent most waste water streams from being dumped into rivers, lakes or oceans without extensive treatment to remove contaminants. Most industrial waste water streams cannot be sewered. The only alternative for disposal of many waste water streams is to haul the waste water to an appropriate treatment facility. The transportation expense combined with the expense of treating this volume of waste can be excessive.
Waste water evaporators were devised to remove much of the water volume from the waste water stream, to lower the hauling costs of transporting this volume and weight of water to a waste water treatment station. Waste water evaporators transfer heat to the waste stream in a variety of methods to evaporate water from the waste. In one such evaporator, a vat is filled with the waste and a heat source is applied at the bottom of the vat to transfer heat through the vat to evaporate water from the waste. Another method is to have a heating tube coiled inside the vat, and to direct a heating fluid through the tube such that heat is transferred through the tube to the waste stream. A third method is to provide electrodes within the vat to heat the waste stream.
Traditional evaporators pump more waste water into the vat when the waste level in the vat has dropped to a set point level. Over time, evaporation of the water from the vat with added waste water increases the concentration of non-evaporated constituents in the vat. As the concentration of solids in the water increases, the likelihood that more contaminants will be carried with the evaporated water also increases. The increasing solids concentration also decreases the efficiency of the evaporator because the applied heat is absorbed by the accumulating solids in the vat. Also, the solids line the vat surface and cover the heating elements, tubes and other components in the vat such as level sensors. The accumulating solids on the surfaces of the vat, as well as heating tubes and elements, create a resistance to heat transfer which increases the overall cost of operation, since more energy must be expended in order to transfer heat through the solids to the waste water in the vat, and since heat will be absorbed by the solids.
A further problem with current evaporators is that the solids must periodically be removed from the vat. Drains are typically provided in the vat to remove sludge from the vat, however, this sludge must be at least 60% water in order to permit the sludge to flow through the drain. Sludge that remains coated on the vat and other elements and components must be cleaned periodically, usually with water. The sludge and cleaning water must be hauled away, which increases the cost of operating the evaporator.
A solution to the problems with evaporators has been the introduction of thermo-oxidizer evaporators. In such systems, the waste water stream is not heated in a vat, but instead is injected into a combustion chamber. The waste water stream is directed at the flame, which rapidly evaporates water in the stream and combusts organic constituents in the stream. The water vapor is directed out of the combustion chamber, and solids comprising inorganic constituents and dry ash collect at the bottom of the combustion chamber. The expense of transporting a heavy waste water stream is avoided, and many contaminants are thermally destructed or eliminated by combustion. The dry ash which collects at the bottom of the combustion chamber must be periodically removed, but the dry constitution of this ash facilitates removal, compared to the wet sludge which typically remains in vat evaporators, Further, there are no heating elements or tubes within the combustion chamber, heat does not have to be transferred through the walls, and solids accumulate at the bottom in the thermo-oxidizer evaporator and do not cause the same heat transfer efficiency problems as with typical vat evaporators.
A thermo-oxidizer evaporator is provided with a combustion chamber, burners, and waste water injection system. The waste water injection system is preferably adapted to atomize the waste water stream. The burners direct a flame near the waste water stream as it enters the combustion chamber so as to evaporate water in the waste water stream and combust contaminants in the waste water stream. The water leaves the combustion chamber as vapor, and contaminants collect at the bottom of the combustion chamber as dry ash. Heat exchange apparatus heats air prior to injection into the combustion chamber. A temperature controller controls fuel and air flow into the combustion chamber. Baffles in the combustion chamber increase the residence time to facilitate the settling of solid constituents from the gas stream leaving the combustion chamber.
A method for treating liquid waste according to the invention can include the steps of injecting the liquid waste into a combustion chamber; contacting the liquid waste with heat from the flame adapted to evaporate water in the liquid waste and to combust combustible materials in the liquid waste, where the flame is preferably generated by burners receiving air and fuel from supply lines. The air is preferably preheated by performing heat exchange with hot gases in the combustion chamber. The supply of air and fuel to the burners can be controlled by a controller responsive to at least the temperature in the combustion chamber. The liquid waste can be contacted in the combustion chamber with structure adapted to increase the residence time of the waste in the thermo-oxidizer evaporator to facilitate settling of particulates and combustion of combustible materials.